It would be highly desirable to be able to detect the presence of a mobile terminal such as a cell phone in the vicinity of one or more selected locations, and moreover, to then identify the particular cell phone (e.g., to locate and identify a particular individual using his or her cell phone) which has been detected. In particular, it would be highly desirable to be able to do so with relatively low cost.
For example, such a capability would be highly useful for providing location-dependent advertising. In one embodiment of location-dependent advertising, a store in a shopping mall might install a detecting device near a particular store display. When a mobile phone user passed near the display, the detecting device could then advantageously detect the presence of a mobile phone nearby (for example, within a distance of five meters) and, preferably, could also identify the associated telephone number. The store computer could then send a message with an advertisement directly to the given mobile phone user.
Moreover, it is well known that a cell phone, such as, for example, a cell phone using the GSM (Global System for Mobile communications) standard, generates detectable radio interference. (The GSM wireless communications standard is fully familiar to those of ordinary skill in the art.) In fact, it is well known to users of GSM cell phones that if the cell phone is used in the vicinity of an electronic device (such as, for example, a radio receiver, stereo system, TV set, a wired/fixed telephone or even another GSM cell phone), the radio transmissions from the GSM cell phone may be inadvertently “picked up” by the electronic device and a signal proportional to the envelope of the radio transmission may be produced inside the electronic device. In fact, this typically unwanted signal may even disrupt the operation of the electronic device. (For example, it is particularly well known that GSM phones present a potential hazard for wearers of heart pacemakers, as the GSM signal may disrupt proper pacemaker operation if the phone is very near to the wearer's chest.)